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16 | NewScientist | 1 June 2013 HUMBLE backyard stargazers have staged a cosmic stakeout, besting a measurement made by NASA’s famous Hubble telescope. The measurement is the distance to SS Cygni, a star system consisting of a white dwarf plus a companion. The strong gravity from the dwarf strips material from the companion, forming a whirling, flattened accretion disc. This regularly ignites in outbursts that occur every 49 days or so. But the distance to SS Cygni measured by Hubble, of 520 light years, suggests a disc brightness that, when plugged into the leading model of accretion disc formation, would put it in a permanent state of explosion. To solve the conundrum, Gregory Sivakoff of the University of Alberta in Canada and colleagues asked amateur Chemical roots of sexual attraction IT IS known as the happiness chemical, but could serotonin also influence sexual preference? It certainly seems to in mice. Serotonin is normally associated with mood – particularly feelings of well-being. But when Yi Rao of Peking University in Beijing, China, and his colleagues genetically engineered female mice so that they could no longer make or respond to serotonin, it appeared to affect their sexuality. Although they would still mate with males if no other females were present, given the choice, the rodents preferred sniffing and mounting females (PNAS, DOI: 10.1073/pnas.1220712110). This is the first time that sexual preference has been reversed in female mammals without the use of sex hormones. Serotonin can modulate olfaction, but the team ruled this out. Instead, it seems the chemical has a more central role in controlling sexual preference. No sugar, thanks, it’s all bitterness to a cockroach IN THE race for world domination, cockroaches have scored another point against Homo sapiens. Their weapon? They evolved a distaste for sugar. In the mid-1980s, pest-control companies introduced roach-killing cocktails of food mixed with slow-acting insecticide. Lured in by the food, the roaches ate the heady mix, returned to their nests and died several hours later, spreading the poison when their nest-mates devoured their faeces and bodies. By 1993, however, the toxic bait was becoming ineffective. Coby Schal of North Carolina State University in DENNIS KUNKEL MICROSCOPY, INC./VISUALS UNLIMITED/CORBIS IN BRIEF Hobbyist stakeout solves star mystery stargazers to alert them when SS Cygni ignited so that they could point two high-end telescopes at the system to measure its distance from Earth. These measurements were more precise than Hubble’s, putting the distance at 370 light years (Science, doi.org/mmv). When plugged into the disc model, the observed, periodic outbursts were predicted. This suggests the model is correct, a relief for astronomers who use it to explain many phenomena. Raleigh says common German cockroaches evolved an aversion to the glucose it contained. The survivors passed on their aversion to their descendants, and Darwinian selection made it more common. Schal and his colleagues have found that glucose tastes bitter to some roaches, which have tiny hairs that sense sweet and bitter. Sweet normally attracts them, but in some roaches bitter taste hairs also respond to glucose, repelling them. They link the smell of the bait to bitter taste, so in a Pavlovian response learn to avoid the food from its smell (Science, doi.org/mmg). New bait could substitute fructose for glucose, but Schal predicts the pests would evolve a distaste for fructose in response. “The arms race between us and cockroaches is a very dynamic playing field,” he says. PANICKING ants could help design buildings that can be evacuated faster in emergencies. The positioning of exits and pillars affects escape times but there is little data on what really works best because it is unethical to fake an emergency to make people panic. To get around this, Majid Sarvi from Monash University in Melbourne, Australia, turned to social insects. Sarvi used repellent to make ants flee from various structures. In a computer simulation of human behaviour in the layouts exited most swiftly by ants – those with exits in corners rather than in the middle of walls, for example – evacuation times were reduced by up to 160 per cent (Transportation Research C, doi.org/mk8). For the fastest exit, follow the ants
